Abstract

The thermally induced order-to-disorder transition of a monolayer of krypton (Kr) atoms adsorbed on a graphitesurface is studied based on a coarse molecular-dynamics (CMD) approach for the bracketing and location of the transition onset. A planar order parameter is identified as a coarse variable, , that can describe the macroscopic state of the system. Implementation of the CMD method enables the construction of the underlying effective free-energy landscapes from which the transition temperature, , is predicted. The CMD prediction of is validated by comparison with predictions based on conventional molecular-dynamics (MD) techniques. The conventional MD computations include the temperature dependence of the planar order parameter, the specific heat, the Kr–Kr pair correlation function, the mean square displacement and corresponding diffusion coefficient, as well as the equilibrium probability distribution function of Kr-atom coordinates. Our findings suggest that the thermally induced order-to-disorder transition at the conditions examined in this study appears to be continuous. The CMD implementation provides substantial computational gains over conventional MD.

Received 04 August 2008Accepted 02 October 2008Published online 11 November 2008

Acknowledgments:

This work was supported by the National Science Foundation through Grant Nos. CTS-0205584, ECS-0317345, CTS-0417770, and CBET-0613501 (M.A.A. and D.M.) and by the U.S. DOE through CMPD and DARPA (I.G.K.). The work of M.A. and V.A.F. was funded by DARPA DSO (Cindy Daniell, PM) managed by the AFOSR Computational Mathematics Program (Fariba Fahroo, PM) under Robust Uncertainty Management Contract No. FA9550-07-C-0024. Useful discussions with G. Hummer and S. M. Auerbach are gratefully acknowledged. The DyNARUM team at United Technologies Research Center also is acknowledged for introducing us to the Kr-on-graphite problem.